Two-step rocker arm having roller element cam followers

ABSTRACT

The invention provides a two-step rocker arm assembly for use in an internal combustion engine in which a plurality of two-step rocker arm assemblies enable the engine poppet valves to switch between two lift profiles. The two-step rocker arm assembly of the present invention has an inner rocker arm assembly and an outer rocker arm assembly. The outer rocker arm assembly is characterized as having two rail portions spaced from each other forming an open space within which at least a portion of the inner rocker arm is disposed. Each of the rail portions and the inner rocker arm assembly has a generally cylindrical roller cam follower rotatably affixed thereto. Preferably, each of the roller element cam followers will be shaft mounted, the shafts being welded to the respective inner rocker arm and outer rocker arm for increased structural rigidity.

TECHNICAL FIELD

This invention relates to a two-step switchable rocker arm for an internal combustion engine.

BACKGROUND OF THE INVENTION

Some prior art valvetrains are selectively adjustable to vary the amount of valve travel during opening. Typically, such valvetrains are selectively adjustable between a low-lift mode, in which the valvetrain causes an engine poppet valve to open a first predetermined amount (with lost motion), and a high-lift mode, in which the valvetrain causes the poppet valve to open a second predetermined amount that is greater than the first predetermined amount. This transitioning is accomplished with the use of a two-step rocker arm having an inner and an outer rocker arm assembly operating in contact with a camshaft having two distinct cam profiles, a low lift cam and a high lift cam. Prior art two-step rocker arms employ a roller element cam follower cam interface at the inner rocker arm, which is typically utilized for low lift mode. Additionally, prior art two-step rocker arms employ a sliding cam interface for the outer rocker arm, which is typically selectively lockable to the inner rocker arm to allow the high lift mode of operation.

SUMMARY OF THE INVENTION

The present invention relates to a valvetrain configuration in an internal combustion engine in which a plurality of two-step rockers enable the engine poppet valves to switch between two lift profiles.

Provided is a two-step rocker arm assembly having a movable outer rocker arm characterized by two rail portions spaced a distance apart from one another and defining an open space therebetween. Each of the rail portions has a generally cylindrical roller element cam follower rotatably attached thereto for engagement with a high-lift cam. An inner rocker arm is movably connected to the outer rocker arm such that at least a portion of the inner rocker arm is in the open space. The inner rocker arm has another generally cylindrical roller element cam follower rotatably attached thereto for engagement with a low-lift cam. The outer rocker arm and the inner rocker arm are selectively lockable for unitary movement.

Also provided is a valvetrain having a camshaft with a low-lift cam and two high-lift cams, the two high-lift cams being on opposite sides of the low-lift cam. Also included is a movable outer rocker arm characterized by two rail portions spaced a distance apart from one another and defining an open space therebetween. Each of the rail portions has a generally cylindrical roller element cam follower rotatably attached thereto for engagement with a respective one of the high-lift cams. Additionally, an inner rocker arm is movably connected to the outer rocker arm such that at least a portion of the inner rocker arm is in the open space. The inner rocker arm has a generally cylindrical roller element cam follower rotatably attached thereto for engagement with the low-lift cam. The outer rocker arm and the inner rocker arm are selectively lockable for unitary movement.

The above features and advantages, and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional fragmentary view of a valvetrain assembly illustrating a two-step rocker arm in accordance with the present invention; and

FIG. 2 is a partial isometric view of the valvetrain assembly shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to the recent art on switchable rockers, such as commonly assigned U.S. Pat. No. 6,769,387, entitled “Compact Two-Step Rocker Arm”, and hereby incorporated by reference in its entirety, the basic kinematic arrangement for a switchable rocker includes two arms pivoted at one end using a pin joint, therefore, having a freedom of relative rotation with respect to each other. This rotational motion takes place against a biasing spring placed between the arms, preloaded in assembly urging each arm to rotate away from each other. Each arm encompasses a follower surface or cam interface in contact with a respective cam lobe. The two cam lobes, defined as the high-lift cam lobe and the low-lift cam lobe, act simultaneously on their respective cam interface. The arm that follows the motion of the low-lift cam lobe is pivoted at one end and contacts the engine poppet valve at the other end. In the low-lift mode of operation of the engine poppet valve, the low-lift cam lobe is the controlling motion generator. In this mode, the high-lift cam lobe displaces its respective arm to idle in relative rotational motion centered around the pin joint. In the high-lift mode of operation of the engine poppet valve, a mechanical-locking device is hydraulically actuated to prevent the relative rotational motion of the two arms with respect to each other. Because the displacement of the high-lift cam lobe is larger than the low-lift cam lobe, the high-lift cam lobe becomes the controlling motion generator. The locking device may be a circular pin located on one of the arms, hydraulically actuated against a biasing spring, and urged towards a receiving circular opening located on the other arm. Upon decrease of the actuation pressure, the actuation pin is retracted out of the receiving opening, thereby switching the control of the engine poppet valve motion back to the low-lift cam lobe.

The present invention specifically relates to a valvetrain configuration employing a two-step rocker arm having roller element cam followers.

Referring to FIGS. 1 and 2, the valvetrain assembly 10 includes a camshaft 12 engaged with a two-step rocker arm (or two-step rocker arm assembly) 14 for actuating a poppet valve 16 against the force of a poppet valve spring 18. A hydraulic lash adjuster 20 is positioned within a bore or aperture 22 in a cylinder head 24, shown in FIG. 1, to engage the two-step rocker arm assembly 14 in a manner to compensate for lash and, with certain designs, selectively deactivate the poppet valve 16. The FIGS. 1 and 2 show a single two-step rocker arm 14, poppet valve 16, and hydraulic lash adjuster 20, but, of course, in an operating engine, multiples of each would be provided for each cylinder.

The camshaft 12 includes low lift cams 26 and high lift cams 28. The two-step rocker arm assembly 14 includes an inner rocker arm assembly 30 and an outer rocker arm assembly 32 which are pivotably joined by a generally cylindrical pivot shaft 34. The inner rocker arm assembly 30 includes an inner rocker arm 36. The outer rocker arm assembly 32 includes an outer rocker arm 38 characterized by two rail portions 40 longitudinally oriented with respect to the rocker arm assembly 14, spaced a distance apart from one another, and forming an open space 42 therebetween. Tie bar portions 44 of the outer rocker arm assembly 30 interconnects the two rail portions 40. The inner rocker arm 36 and the outer rocker arm 38 are preferably investment cast. The inner rocker arm assembly 30 is at least partially located within the open space 42.

The pivot shaft 34 is press fit into the inner rocker arm 36. The pivot shaft 34 has a close, but non-interference fit, through bores or apertures 46 in each of the rail portions 40 of the outer rocker arm 38. The inner rocker arm 36 includes a valve stem contact pad 48 at a first end 50 adjacent to the pivot shaft 34. The press fit design for the pivot shaft 34 allows for a traditional valve to rocker arm interface by virtue of the geometry at the valve stem contact pad 48. Alternatively, the pivot shaft 34 may be press fit into the outer rocker arm apertures 46 and have a close, but non-interference fit, to the inner rocker arm 36. The poppet valve 16 has a rotational symmetry about an axis A, shown in FIG. 1. The pivot shaft 34 is disposed in relation to the contact pad 48 such that the axis A substantially intersects the pivot shaft 34.

The inner rocker arm assembly 30 also includes a roller element cam follower 52, shown in FIG. 2, rotatably disposed in an opening defined by the inner rocker arm 36. The inner rocker arm assembly 30 also includes locking pins (not shown) used to selectively prevent relative motion between the inner rocker arm 36 and the outer rocker arm 38, thereby selectively providing lost motion as described above. Accordingly, lost motion may be achieved in the two-step rocker arm assembly 14 thereby providing low-lift, high-lift and zero-lift modes. The operation of a two-step rocker arm is described in more detail in the above referenced U.S. Pat. No. 6,769,387, entitled “Compact Two-Step Rocker Arm”.

The inner rocker arm 36 also includes a valve stem guide ear 54 on each side of the valve contact pad 48. The inner rocker arm 36 also defines a boss portion, or pivot interface, 56 against which the hydraulic lash adjuster 20 abuts, and about which the inner rocker arm 36 is pivotable. Within the scope of the claimed invention, rail portions 40 and tie bar portions 44 may or may not be part of a one-piece outer rocker arm. For example, the rail portions 40 and tie bar portions 44 may be separate members rigidly connected to one another to form the outer rocker arm 38.

The roller element cam follower 52, shown in FIG. 2, is configured for engagement with the low-lift cam 26, which causes the inner rocker arm assembly 30 to pivot about the hydraulic lash adjustor 20 at the pivot interface 56. The roller element cam follower 52 is rotatable with respect to the inner rocker arm 36 on an axle 58, shown in phantom in FIG. 1. The axle 58 is preferably laser welded in place for increased structural rigidity of the inner rocker arm assembly 30. A torsion spring 60, shown in FIG. 1, engages both the inner and outer rocker arms 36, 38 for biasing the inner and outer rocker arms 36, 38 in an opening direction about the pivot shaft 34.

The outer rocker arm assembly 32 also includes a roller element cam followers 62 located in openings defined by each rail portion 40 of the outer rocker arm 38. Each of the roller element cam followers 62 is rotatable with respect to the rail portions 40 on axles 64. Each of the axles 64 are preferably laser welded to the respective rail portion 40 for increased structural rigidity of the outer rocker arm assembly 32. The roller element cam followers 62 contact the high lift cams 28 for maximum lift of the poppet valve 16 when the two-step rocker arm assembly 14 is locked, that is, when the two-step rocker arm assembly 14 is not operating in “lost motion”, or low lift, mode. Those skilled in the art will recognize other methods of securing the axles 58 and 64 while still remaining within the scope of the present invention. In the preferred embodiment the roller element cam followers 52 and 62 will have an equal diameter.

By employing the roller element cam followers 52 and 62 within both the inner and outer rocker arm assemblies 30 and 32, respectively, the friction characteristics of the cam interface may be reduced over a sliding cam interface. Additionally, by employing the roller element cam followers 52 and 62, the two-step-rocker arm assembly 14 of the present invention may require less lubrication than a design that employs both a sliding cam interface and roller element cam followers. The two-step rocker arm 14 of the present invention enables the material properties of the camshaft 12 to be optimized for contact with a single type of material, the roller element cam followers 52 and 62, rather than two different materials, e.g. a roller element cam follower of one material and a sliding cam interface of another material.

While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims. 

1. A two-step rocker arm assembly comprising: a movable outer rocker arm characterized by two rail portions spaced a distance apart from one another and defining an open space therebetween, each of said rail portions having a generally cylindrical roller element cam follower rotatably attached thereto for engagement with a high-lift cam; wherein each of said roller element cam followers is disposed at least partially within said outer rocker arm and is rotatable attached to a respective one of said rail portions via an axle, said axle being welded to said respective rail portion; an inner rocker arm movably connected to said outer rocker arm such that at least a portion of said inner rocker arm is in said open space, said inner rocker arm having another generally cylindrical roller element cam follower rotatably attached thereto for engagement with a low-lift cam; and wherein said outer rocker arm and said inner rocker arm are selectively lockable for unitary movement.
 2. (cancelled)
 3. The two-step rocker arm assembly of claim 1, wherein said roller element cam follower disposed at least partially within said inner rocker arm is rotatably attached to said inner rocker arm via an axle, said axle being welded to said inner rocker arm.
 4. The two-step rocker arm assembly of claim 1, further comprising: a torsion spring operatively connected to said inner rocker arm and said outer rocker arm; and wherein said torsion spring biases said outer rocker arm in a direction to maintain contact between each of said roller element cam follower and its respective high-lift cam or low lift cam.
 5. The two-step rocker arm assembly of claim 1, wherein said generally cylindrical roller element cam followers have substantially equal diameters.
 6. The two-step rocker arm assembly of claim 1, wherein said inner rocker arm is characterized by a pivot interface for contacting a portion of a hydraulic lash adjustor upon which said inner rocker arm is pivotable.
 7. The two-step rocker arm assembly of claim 1, further comprising: a generally cylindrical pivot shaft about which said inner rocker arm and said outer rocker arm are pivotably movable with respect to one another; a contact pad operable to engage a poppet valve, wherein said poppet valve has rotational symmetry about an axis; and wherein said pivot shaft is positioned with respect to said contact pad such that when said contact pad engages said valve, said pivot shaft substantially intersects said axis of said poppet valve.
 8. The two-step rocker arm assembly of claim 1, wherein said inner rocker arm and said outer rocker arm are investment cast.
 9. A valvetrain comprising: a camshaft having a low-lift cam and two high-lift cams, said two high-lift cams being on opposite sides of said low-lift cam; a movable outer rocker arm characterized by two rail portions spaced a distance apart from one another and defining an open space therebetween, each of said rail portions having a generally cylindrical roller element cam follower rotatably attached thereto for engagement with a respective one of said high-lift cams; wherein each of said roller element cam followers is disposed at least partially within said outer rocker arm and is rotatable attached to a respective one of said rail portions via an axle, said axle being welded to said respective rail portion; an inner rocker arm movably connected to said outer rocker arm such that at least a portion of said inner rocker arm is in said open space, said inner rocker arm having a generally cylindrical roller element cam follower rotatably attached thereto for engagement with said low-lift cam; and wherein said outer rocker arm and said inner rocker arm are selectively lockable for unitary movement.
 10. (cancelled)
 11. The valvetrain of claim 9, wherein said roller element cam follower disposed at least partially within said inner rocker arm is rotatably attached to said inner rocker arm via an axle, said axle being welded to said inner rocker arm.
 12. The valvetrain of claim 9, further comprising: a torsion spring operatively connected to said inner rocker arm and said outer rocker arm; and wherein said torsion spring biases said outer rocker arm in a direction to maintain contact between each of said roller element cam follower and a high-lift cam.
 13. The valvetrain of claim 9, wherein said generally cylindrical roller element cam followers have substantially equal diameters.
 14. The valvetrain of claim 9, wherein said inner rocker arm is characterized by a pivot interface for contacting a portion of a hydraulic lash adjustor upon which said inner rocker arm is pivotable.
 15. The valvetrain of claim 9, further comprising: a generally cylindrical pivot shaft about which said inner rocker arm and said outer rocker arm are pivotably movable with respect to one another; a contact pad operable to engage a poppet valve, wherein said poppet valve has rotational symmetry about an axis; and wherein said pivot shaft is positioned with respect to said contact pad such that when said contact pad engages said valve, said pivot shaft substantially intersects said axis of said valve.
 16. A two-step rocker arm assembly comprising: a movable outer rocker arm characterized by two rail portions spaced a distance apart from one another and defining an open space therebetween, each of said rail portions having a generally cylindrical roller element cam follower rotatably attached thereto for engagement with a high-lift cam; an inner rocker arm movably connected to said outer rocker arm such that at least a portion of said inner rocker arm is in said open space, said inner rocker arm having a generally cylindrical roller element cam follower rotatably attached thereto for engagement with a low-lift cam; wherein said outer rocker arm and said inner rocker arm are selectively lockable for unitary movement; wherein each of said roller element cam followers, disposed at least partially within said rail portions, is rotatably attached to its respective rail portion via an axle, said axle being welded to said rail portion; and wherein said roller element cam follower disposed at least partially within said inner rocker arm is rotatably attached to said inner rocker arm via an axle, said axle being welded to said inner rocker arm.
 17. The two-step rocker arm assembly of claim 16, wherein said generally cylindrical roller element cam followers have substantially equal diameters. 